A portable electronic object, such as an electronic device or, for example, a portable timepiece, includes a case generally formed of a middle part closed by a back cover and by a glass. Inside the case is arranged a timepiece movement, which may be electromechanical or totally electronic. This timepiece movement is arranged to provide time information, said time information being displayed via analogue or digital display means. The timepiece further includes control means enabling the user to interact with said timepiece.
In general, the control means take the form of push buttons or a crown acting mechanically on said timepiece movement. These push buttons and crowns may be supplemented with a touch interface. This touch interface is used to improve the interactivity of the timepiece and to simplify handling especially when the timepiece proposes a significant number of menus and functions.
The touch interface may be a resistive touch interface or a capacitive touch interface. For the case of a capacitive touch interface, this may take the form of an electrode placed on the lower face of the glass, the glass being an electrically non-conductive element. The electrode is subjected to an electric field. When the user wishes to activate the interface, he exerts a contact force on the external face of the glass, preferably with his finger. This means that the contact force can be a tap or a light touch. This contact causes an additional capacitance to appear, formed between said electrode and the finger, which is an electrically conductive element. This variation in capacitance is detected by the electronic timepiece movement which will act according to its programming. This touch interface is created on the watch glass and not on the case since the latter is generally made of metal and is therefore electrically conductive. The case does not permit a capacitance to appear.
However, these touch interfaces arranged on the timepiece glass have the drawback of not permitting optimum visualisation of data. Indeed, the fact of having a touch interface arranged on the timepiece glass means that the user has to regularly place his fingers on the glass. Consequently, visualisation of the data displayed on the dial is regularly reduced by the user's fingers. The user therefore has more difficulty in reading the data provided by the timepiece.
Further, these touch keys are generally created by depositing a metal layer such as an indium-tin-oxide (ITO) layer on a substrate such as the glass. One drawback of applying this type of ITO layer onto the glass is that this is a complex and expensive operation. Consequently, extremely rigorous manufacturing is required to obtain a good production yield.